Most previous studies of stomatal behaviour on isolated epidermis of Commelina communis have been carried out in media of pH 6.5-7.0. In the present investigation we have used a wide range of pH values obtained with several different buffers, and have paid special attention to the response of the epidermis to incubation in media of pH 4.0-5.0. Within this region of pH, all the cells of the epidermis apart from the guard cells were severely damaged, a condition leading to considerably enhanced stomatal openings even in media containing low concentrations (1 mM) or completely lacking inorganic cations. The guard cells appeared to continue to function normally, with stomatal apertures changing in response to light and CO2, and the cells showing the expected solute potential changes and potassium accumulation as opening occurred. The stimulation of opening might, in part, be attributable to the removal of pressure from the surrounding cells.
Exposure of epidermis to a pH of 4.5 for 1 1/2 hours proved to be a highly effective method of destroying all the cells apart from the guard cells, which apparently remained fully functional. This is a quick and reliable way of‘isolating’ stomata which could prove invaluable in future studies of their physiology and metabolism. A comparison of stomatal responses to solutes in the medium for epidermis with all cells intact and for epidermis with isolated stomata suggests a role for the subsidiary cells in regulating solute entry into the guard cells.
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